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Arch Bridge - Shell model

8 REPLIES 8
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Message 1 of 9
mgt89
1179 Views, 8 Replies

Arch Bridge - Shell model

Greetings friends I need your help again.

 

I´m trying to build a shell model of an arch bridge, using ARSA 2014.The model will be used for a modal analysis bur unfortunately I´m facing some problems. I have created a bar model that dint deliver the best results. 

 

I´ve attached some photos (image 1, 2,3 and 4) of the bridge for better understanding of the problem. The model was build the following way:

 

1º Draw all polyline contour according to the project. I´ve made an effort to replicate the real geometry the best way.

2º Define Panels to each contour. The height for the arch is variable, so I´ve created a thickness that is variable along the line for each panel of the arch.

 

Problems:

 

1- The first problem that I am having is in the creation of the mesh. As you can see it gives a lot of problems around the edges. I have used some suggestions that I´ve found on the forum. But I´, still getting some weird results. How can I fix that?

 

2- I have no idea of how to model the deck. And how to make the connection to the columns. The deck is made of a slab with 4 beams connected (image 4) I was thinking in finding the center of gravity of each beam and connect it to the columns through a rigid link and them make  the beam and the slab with bars. Would that work? What's the best approach. 

 

I would really appreciate some help 

 

Attachment: http://we.tl/emSf4XxWUP

8 REPLIES 8
Message 2 of 9
richardwhitfield
in reply to: mgt89

Hello,

 

I've had a very quick look at the model and have a couple of pointers that may assist...

 

1. Extend the vertical members out to the edge of the arch...although Robot has a powerful meshing algorithm it can be a real pain to get complex meshes to work so simplify wherever possible (looking at the photos there doesn't appear to be as large an offset as it modelled).  This will also help with creating the geometry as you can snap only to object endpoints which leads me to point 2...

 

2. Your vertical panels do not finish at the same point as the arch panels which is why Robot is having a difficult time in meshing these areas.  I would love for panel input to be tabulated in Robot but it's not a feature yet...

 

3. For the deck slab it depends what you need to use it for...if you are just trying to replicate the stiffness then you can model the beams with offsets (rather than manually defining rigid links), however you will get coincident tension/compression in the slab as well as the beam moments to account for the offset so don't use that approach if you are looking at moments in the beam/slab.  If you need the moments but wish to model the additional stiffness from T beam action you can model the beams at their centreline and in the sections window (where you define the beam parameters) select 'reduction in moment of inertia' and increase the value above 1 as required - work out the moment of inertia for the T beam and the centreline beam options and divide one by the other to get the relative increase (some design codes will give guidance on the effective flange width for a T beam that can be used).

 

I hope this helps.

 

Rgds,

 

Rich

Message 3 of 9
richardwhitfield
in reply to: mgt89

I ran the roundup addin and remeshed with a simple mesh and it's more coherent now...see link below.

 

There was also no thickness assigned to the panels and hence no material so I have temporarily made this 200thk concrete.

 

https://mottmacaustralia.sharefile.com/d/sf76de17213d4d65b

 

Rgds,

 

Rich

Message 4 of 9
mgt89
in reply to: richardwhitfield

This is amazing thanks a lot for the help. How did you manage to fix it? I don't know what the "roundup addin" is 😛

 

Plus I did not understand your point 2. Did you fix that on the model that you gave me? I created first the arch panels and then the columns at the same x and z coordinates. Shouldn't that be enough for them to finish at the same position?

 

I will now try to build the deck I´m sure I´ll have some doubts again hope you can help me 😄

 

But just to be sure. I should connect all the columns with 4 bars, and to each bar I will give the beam cross sections? Calculating beff with EC2 if necessary?

after that i use an offset for the real center of gravity?

and create the slab with a panel connecting the bars?

Thanks a lot. 

Message 5 of 9
Rafal.Gaweda
in reply to: mgt89

I don't know what the "roundup addin" is 😛

 

You will find it here:

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/useful-addins-for-Robot-API/td-p/3899448

 

 



Rafal Gaweda
Message 6 of 9
Rafal.Gaweda
in reply to: Rafal.Gaweda

Ad.1 Coons meshing is less sensitive for different kinds of inaccuracies.

(BTW you have not found on forum hints about not using kinematic links and regular mesh)

IN fact it is not required to correct your model, just change meshing parameters as shown below. To obtain the best mesh I suggest to mesh vertical panels firts then the rest.

 

coonsbridge.jpg

 



Rafal Gaweda
Message 7 of 9
Rafal.Gaweda
in reply to: Rafal.Gaweda

Message 8 of 9
mgt89
in reply to: mgt89

Hi thanks for all the suggestions. Just a really stupid question 😛 what do you mean by Ad.1, Ad. 2/3?

 

Thanks

 

 

Message 9 of 9
Rafal.Gaweda
in reply to: mgt89

Just a really stupid question 😛 what do you mean by Ad.1, Ad. 2/3?

 

Upps sorry, in english it should be  Re: (re:) "REGARDING", "in reference to"



Rafal Gaweda

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